Utilization of pulsed laser sources has increased in industrial and scientific applications. In particular, applications of ultrashort laser technology have increased over the last few years in metrology, imaging and material processing applications. Fiber-based ultrashort systems are now well established for numerous applications, and are particularly well suited for high repetition rate applications at low-medium pulse energy. However, in either passive or gain fiber, the peak power of the amplified pulse is constrained because of the pulse distortion and signal shifting out of the gain spectrum caused by nonlinear effects, for example Raman shifting. Chirped pulse amplification is often used to greatly extend the capability of fiber systems. Pulses are temporally stretched, thereby lowering the peak power, then amplified and recompressed. Such constraints also apply to other optical media as the pulse energy scales up, for example Nd:based bulk optical amplifiers.
The following patents, published patent applications, and publications relate, at least in part, to fiber lasers and amplifiers, ultrashort laser material processing, optical measurement techniques, and/or various arrangements for generating groups of laser pulses: U.S. Pat. No. 6,339,602; U.S. Pat. No. 6,664,498; U.S. Pat. No. 6,954,575; U.S. Pat. No. 7,088,878; U.S. Pat. No. 7,580,432; U.S. Patent Application Pub. No. 2002/0167581; U.S. Patent Application Pub. No. 2003/0151053; U.S. Patent Application Pub. No. 2005/0218122; U.S Patent Application Pub. No. 2010/0272137; WIPO Pub. No. 2009146671; Strickland and G. Mourou, Opt. Commun. 56, 219 (1985)., H. Hofer et. al., Opt. Lett. 23, 1840 (1998); M. E. Fermann et al., Phys. Rev. Lett., 84, 2000 (2010).
Various applications require multiple beams or pulse trains. In such applications, pulses in the multiple beams may have a well-defined relative time interval, requiring some level of synchronization. Time domain measurements are an example. More specifically, with optical time gating or correlation techniques, a first beam is used for optical interaction with a sample, and a second beam is used for a time gating or correlation function. Specifically, for an ultrashort measurement, synchronization is needed to obtain the desired time resolution. Terahertz spectroscopy, optical pump-probe spectroscopy and other time gated imaging processes utilizing an ultrashort pulse laser fall into this application category.
Conventional laser-based systems used for such applications are often designed to create pulses with sufficiently high energy, and to subsequently divide the beam into multiple beam paths in the application system.
Amplification of high intensity optical pulses in an optical fiber and other gain media, for example regenerative amplifiers, ultimately requires consideration of nonlinearity. Often the pulse energy constraint results in limited average power. Increasing the average power without loss of pulse energy would be a useful improvement for high peak power pulse laser systems.
Therefore, a need exists to extend the peak power capability of pulsed laser sources, including fiber based systems, regenerative amplifiers, thin disk lasers, and the like.